The present invention relates to an avionics system of an aircraft comprising line replaceable units that can exchange messages between them via one or more communication buses and a monitoring device for monitoring the messages exchanged between a line replaceable unit of the avionics system and at least one other unit of the avionics system.
The various apparatuses of an avionics system take the form of units which can be plugged into a rack so as to be able to be replaced, for example in case of failure, easily and very rapidly, even if the aircraft concerned is in flight. Such units are commonly referred to in the aircraft field by their acronym LRU, standing for Line Replaceable Unit. In the present description, the LRU units are called line replaceable units.
For example, an avionics system dealing with all the communication functions between the ground and the aircraft comprises a unit called ATSU, the acronym for Air Traffic Services Unit and a radio unit called VDR, the acronym for Very High Frequency Data Radio (VHF data radio). Each of these units is housed in an LRU unit. The first incorporates an air/ground communication router making it possible to switch applications of AOC (Airline Operational Control) type and of ATC (Air Traffic Control) type, exchanging between the crew of the airplane and the airline for the AOC applications, on the one hand, and the air control entities for the ATC applications, on the other hand Moreover, another function of this ATSU unit is to encode the applications exchanged. As for the second LRU unit (of VDR type), it is linked, among others, to the ATSU unit, and serves as physical medium for the exchange of communications between the airplane concerned and the ground in a frequency band corresponding to the VHF band. This VDR radio unit thus makes it possible to exchange voice signals between the airplane and the ground, and digital data via a “datalink” stream.
It is necessary to record the data which are exchanged between the LRU units of an avionics system, for various reasons, if only to check whether each of these LRU units is operating correctly, notably in the case of dense air traffic where messages may not be transmitted because of very high data traffic and to thus be able to resend the messages, and if such is not the case, either to remedy the situation which has provoked the observed malfunction, or, if necessary, to replace the failing unit with another of the same type.
Today, such recordings are made by means of large recorders placed in the cabin of the aircraft and which are linked by specific cables to the different LRU units. This recording process happens to be complex, introduces relatively significant delays and creates interferences between the recorded signals and the operational signals due primarily to the fact that the cables linking the LRU units and the recorder radiate in the manner of an antenna. It is also known practice to use specific recorders placed in the avionics rack. However, here also, this process happens to introduce relatively significant delays and also creates interferences between the recorded signals and the operational signals, as previously due to the length of the cables.
There is therefore a benefit to be gained in having available means for monitoring the messages exchanged between a line replaceable unit (units called LRUs) of an avionics system and at least one other unit of the avionics system which do not present the drawbacks described above and, notably, which do not disturb, through the recording, the operational signals.